So why has Terminator Salvation not performed better in the U.S.? Perhaps changing the original ending was a mistake. Director McGrevealed Salvation's initial ending to Entertainment Weekly (WARNING: SPOILERS):

[John] Connor (Christian Bale) dies, okay? He's dead. And Marcus (Sam Worthington) offers his physical body, so Connor's exterior is put on top of his machine body. It looks like Connor, but it's really Marcus underneath. And all of the characters we care about (Kyle Reese, Connor's wife Kate, etc.) are brought into the room to see him and they think it's Connor. And Connor gets up and then there's a small flicker of red in his eyes and he shoots Kate, he shoots Kyle, he shoots everybody in the room. Fade to black. End of movie. Skynet wins. F--- you!

Bale loved the ending. The studio signed off on it. So why the change? "In the end, it just felt like too much of a bummer," McG explained, before pausing. "Maybe we blew it."